Effects of Phosphate on the Growth of Alexandrium Tamarense at Different Initial Nitrate Concentrations in Laboratory Cultures

The objective of this study is to reveal the effects of phosphate on the growth characteristics of Alexandrium tamarense at three different fixed initial nitrate concentrations [14.29 (low-N), 25.00 (medium-N) and 35.71 mu mol/L (high-N)] in laboratory cultures. Experiments were carried out in three independent batch cultures respectively. The cell density and the specific growth rate were assessed as response parameters. The results show that both the cell density and the specific growth rate of A. tamarense increase with the increase of phosphate concentration in low-N-grown cultures, followed by those in medium-N-grown and high-N-grown cultures. And the highest average cell density in low-N-grown, medium-N-grown, and high-N-grown cultures was 1931x104, 4098x104 and 5871x104 cells/L, respectively. The specific growth rate was 3.73, 7.17 and 8.96 d-1, respectively. The results suggested that blooms of A. tamarense are more likely to form in the high nitrate and phosphate concentration than in the low nitrate and phosphate concentration in the natural marine environment.